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20. Raising Custom Exceptions

Python allows you to create and raise your own exception classes. This improves clarity by signaling specific error conditions.

Defining a Custom Exception​

class NegativeNumberError(Exception):
    pass

def factorial(n):
    if n < 0:
        raise NegativeNumberError("Factorial is not defined for negative numbers")
    result = 1
    for i in range(1, n+1):
        result *= i
    return result

Practice Challenge​

Write a function square_root(n) that raises a NegativeNumberError if n is negative.

Wrap-Up​

  • Custom exceptions make code descriptive and easier to debug.
  • Inherit from Exception for user-defined errors.